Optical array and collimated light distribution

ABSTRACT

High luminance display devices, typically utilized in applications requiring sunlight readability, require unique design methodologies as the thickness approaches a maximum of one-inch. The present invention relates to a high-intensity light generation engine and associated light transmission apparatus for transmitting the light generated by the engine to a remote location. The invention is especially applicable for use in constructing a back lighted display, such as a liquid crystal display (LCD), of minimal thickness, i.e., one-inch or less. A display of minimal thickness is achieved by separating a light source and other peripherals from the display device, using a remote enclosure. Such a display is most suited for use in high ambient lighting conditions where space is at a premium, such as in the cockpit of an aircraft.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field

[0002] The present invention relates to a high-intensity lightgeneration engine and associated light transmission apparatus fortransmitting the light generated by the engine to a remote location. Theinvention is especially applicable for use in constructing a backlighted display, such as a liquid crystal display (LCD), of minimalthickness. In particular, the invention achieves a display of minimalthickness by separating the light source from the display mechanism.Such a display is most suited for use in high ambient lightingconditions where space is at a premium, such as in the cockpit of anaircraft. The inventive light generation engine and associated lighttransmissive apparatus may also be used for other applications besidesilluminating a display, such as for projection displays, ground vehicleinstrument displays, automotive lighting (such as headlights, taillights, panel lights, map lights, and dome lights), airport runwaylights, aircraft interior lighting, and street lights.

[0003] 2. Background Art

[0004] Typically, high luminance displays (e.g. those used in avionicsapplications) are based upon transmissive liquid crystal displays (LCDs)with one or more fluorescent lamps. When packaged in a reflecting cavityand supplemented by light control films, such lamps can be driven atsufficient power levels to generate enough lumens to produce well inexcess of 200 fL out of the transmissive LCD. Typically, these displaysare at least three inches thick when combined with a minimal amount ofelectronics. As more electronics are added to increase functionality,display thickness increases correspondingly. Additionally, for avionicsapplications, the active display area must occupy a large percentage ofthe overall enclosure area since instrument panel space is at a premium.This further complication increases packaging density, and as thepackaging density increases, the thermal design obviously becomes morecritical. Beyond approximately 0.1 watts per cubic inch, active coolingshould be employed, which is generally fan-based, thus furtherincreasing volume.

[0005] There exists a desire to drive the display thickness to less thanone inch for many applications, such as avionics. For avionicsapplications, this would facilitate upgrading a cockpit with newdisplays requiring minimal modification of the cockpit instrument paneland surrounding structural members. Obsolete displays may be removed andreplaced by new displays, including those which relate to the presentinvention, that simply attach over the existing instrument panel. Mostavionics displays protrude in front of an instrument panel by no morethan one inch. This limitation is due to several factors, such as theneed to preclude one display from shadowing another. Anotherconsideration is that displays cannot protrude into the ‘ejectionenvelope’ in fighter and attack planes and also cannot interference withthe controls used by a crewmember (such as, for example, limiting fulltravel of the control yoke).

[0006] To achieve high luminance, high contrast, and high resolution ina conventional display intended for high ambient lighting conditions,considerable display thickness and relatively high-intensity lightsources are required. However, thick displays and the large amounts ofheat generated by high intensity lamps are adverse to certainapplications, such as those for the cockpit of an airplane.

[0007] In view of the foregoing, this invention provides a displaysystem in which the light source is located remotely from a displaydevice, such as an LCD, and its backlight. By separating the lamp,driving electronics and other components from the display device andlocating them remotely, space requirements can be satisfied withoutviolating the severe envelope restrictions for aircraft cockpit-suitabledisplay system elements.

[0008] This invention also provides a high-intensity light enginecomprising a light source and a light collection assembly, and anoptical transmission apparatus for transmitting the light to a remotelocation, such as to a display device.

SUMMARY OF THE INVENTION

[0009] The present invention is directed to a high-intensity lightgeneration engine and associated light transmission apparatus fortransmitting the light generated by the engine to a remote location. Theinvention is especially applicable for use in constructing a backlighted display, such as a liquid crystal display (LCD), of minimalthickness, i.e., one-inch or less. A display of minimal thickness isachieved by separating the light source and other peripherals from thedisplay device. Accordingly, the light source and other lighttransmissive apparatus are comprised in a remote enclosure. Such adisplay is most suited for use in high ambient lighting conditions wherespace is at a premium, such as in the cockpit of an aircraft. Theinventive light generation engine and associated light transmissiveapparatus may also be used for other applications such as projectiondisplays, ground vehicle instrument displays, automotive lighting,airport runway lights, aircraft interior lighting, and street lights.

[0010] In accordance with an illustrative embodiment of this invention,a system for illuminating a display, such as a flat panel display (i.e.an LCD) is provided. Several of the systems functional elements areillustratively listed below:

[0011] A light source for generating light.

[0012] A light collection assembly for collecting the light generated bythe light source and for providing one or more light outputs. Thelight-collecting assembly comprises at least one ellipsoidal mirror, andpreferably eight ellipsoidal mirrors, for reflecting the light generatedfrom the light source to corresponding exit port holes.

[0013] A light guide assembly for collecting light from the lightoutput(s) and transmitting it to a common exit port.

[0014] An optional dimmer for providing a controllable variableattenuation of the light emitted by the light guide assembly common exitport.

[0015] A homogenizer for capturing potentially non-uniform light fromthe optional dimmer or, alternatively, directly from the light guideassembly common exit port, and for providing a uniform irradiance acrossthe homogenizer exit port area. The irradiance across the exit port areagenerated by the homogenizer also has uniform spectral and angularcharacteristics. Note that the homogenizer is preferably tapered, whereits input port is larger than its output port.

[0016] A fiber optic cable assembly for capturing light from thehomogenizer exit port and distributing it to multiple exit ports.

[0017] A collimator element assembly. Each collimator element captureslight from a corresponding light distribution means exit port andprojects light with improved collimation.

[0018] A turn-the-corner assembly that captures the collimated lightprojected by the collimator elements and reverses its propagationdirection in a space-efficient manner while maintaining collimation.

[0019] A waveguide backlight that captures the collimated light from theturn-the-corner assembly and projects it in the direction normal to thebacklight exit face.

[0020] A liquid crystal display (LCD) that transmits the collimatedlight projected by the backlight while modulating it spatially and, innon-monochrome applications, spectrally across the LCD area to form animage.

[0021] A view screen that transmits the light projected by the LCD whiledecollimating (or diffusing) it to project the LCD image to be seen overa wide range of viewing angles.

[0022] As an aspect of this embodiment, the system further comprises oneor more optical light pipes (e.g., a solid cylindrical rod or,alternatively, a square or rectangular cross section solid rod), whereeach light pipe is coupled to a respective exit port hole of thelight-collecting assembly. The light pipes reduce heat concentrationsand ultraviolet radiation, generated by the light-collecting assembly,which would otherwise be fully dissipated in the light guides leading tothe homogenizer. The light pipes are preferably made of a visible lighttransparent heat-tolerant material, such as glass, fused silica orsapphire. Further, each light pipe is preferably coated with either adielectric infrared-reflecting coating, an ultraviolet reflectingcoating or a combination thereof.

[0023] As a further aspect of this embodiment, the waveguide has abottom surface having either a sawtooth or a truncated sawtooth surfacefor directing light out of the waveguide at predetermined angles basedon the size and shape of the sawtooth and truncated sawtooth surfaces.

[0024] As an additional aspect of this embodiment, the system includesan apparatus for redirecting light, such as a turn-the-corner prismassembly, positioned preceding the waveguide. Illustratively, thisassembly has one or more prisms, where each prism includes an inputsurface, an output surface, and in the case where there are a pluralityof prisms, an interface between the prisms (such as a thin adhesive orglue gap) to improve the light-handling efficiency of the assembly. Inparticular, the adhesive preferably has an index of refraction less thanthe index of refraction of the adjacent prisms.

[0025] The system also includes an electromechanical dimmer forattenuating the light entering the homogenizer. The dimmer disposedimmediately preceding the homogenizer entrance port is configured tohave a dimming ratio from 300:1 to 88,500:1. The dimmer comprises a pairof aperture plates, where each plate has a diamond-shaped aperture. Oneof these may include a filter therein. However, differently shapedapertures can also be configured to provide the same function.

[0026] As yet a further aspect of this embodiment, the system furtherincludes an array of collimators, positioned immediately preceding theturn-the-corner prism assembly, for collimating the homogenized light.Illustratively, the collimator comprises an array of tapered cavities,where the array's tapered cavities have either round, square, ortriangular cross-sections, or combinations thereof.

BRIEF DESCRIPTION OF DRAWINGS Brief Description of the Several Views ofthe Drawing

[0027]FIG. 1A is a block diagram of a flat panel display system inaccordance with an embodiment of the present invention.

[0028]FIG. 1B is a bottom perspective view of a portion of the flatpanel display system of FIG. 1A in accordance with the presentinvention.

[0029]FIG. 1C is a top perspective view of a portion of the flat paneldisplay system of FIG. 1A in accordance with the present invention.

[0030]FIG. 2A is an exploded view of a portion of a flat panel displaysystem including brackets and a remote enclosure in accordance with thepresent invention.

[0031]FIG. 2B is a block diagram of a portion of the flat panel displaysystem of FIG. 1A including other peripherals in accordance with thepresent invention.

[0032]FIG. 2C is a bottom perspective view of a special alignment washerin accordance with the present invention.

[0033]FIG. 3 shows a dimmer device optionally used in the flat paneldisplay system of FIG. 1A in accordance with the present invention.

[0034]FIGS. 4A, 4B, and 4C are side elevation, isometric, and assemblyviews, respectively, of the light-collecting assembly of FIGS. 1B and 1Cin accordance with the present invention.

[0035]FIG. 5 is a lamp and cooling assembly of the flat panel displaysystem of FIG. 1A in accordance with an embodiment of the presentinvention.

[0036]FIG. 6 is a lamp and cooling assembly of the flat panel displaysystem of FIG. 1A in accordance with a further embodiment of the presentinvention.

[0037]FIG. 7 is a lamp and cooling assembly of the flat panel displaysystem of FIG. 1A in accordance with yet a further embodiment of thepresent invention.

[0038]FIG. 8 is a perspective view of the homogenizer of the flat paneldisplay system of FIG. 1A in accordance with the present invention.

[0039]FIG. 9 illustrates an embodiment of a square collimator array ofthe flat panel display system of FIG. 1A in accordance with anembodiment the present invention.

[0040]FIG. 10A illustrates an embodiment of a detail of the array ofcollimator elements in the flat panel display system of FIG. 1A inaccordance with a preferred embodiment of the present invention.

[0041]FIG. 10B illustrates an embodiment of a detail of the array ofcollimator elements in the flat panel display system of FIG. 1A inaccordance with an alternate embodiment of the present invention.

[0042]FIG. 11 illustrates an embodiment of a packed triangular aircavity collimator array of the flat panel display system of FIG. 1A inaccordance with a further embodiment of the present invention.

[0043]FIG. 12 illustrates an embodiment of a turn-the-corner assembly ofthe flat panel display system of FIG. 1A in accordance with anembodiment the present invention.

[0044]FIG. 13 illustrates the embodiment of the turn-the-corner assemblyof FIG. 12 including a waveguide in accordance with an embodiment thepresent invention.

[0045]FIG. 14 illustrates a waveguide of the flat panel display systemof FIG. 1A in accordance with the present invention.

[0046]FIG. 15 illustrates a bottom surface of a waveguide having asawtooth surface of the flat panel display system of FIG. 1A inaccordance with an embodiment the present invention.

[0047]FIG. 16 illustrates a bottom surface of a waveguide having atruncated sawtooth surface of the flat panel display system of FIG. 1Ain accordance with a further embodiment the present invention.

[0048]FIG. 17 illustrates a conventional bottom surface of a waveguidehaving a pure stepped or truncated surface.

[0049]FIG. 18 is a side perspective view of a portion of the flat paneldisplay system of FIG. 1A including a cylindrical glass rod and ferrulein accordance with the present invention.

[0050]FIG. 19 illustrates the cylindrical glass rod of FIG. 18 inaccordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0051] Mode(s) for Carrying Out the Invention

[0052] In an illustrative embodiment, the present invention is a highluminance, one-inch thick display system, although display systems withanother thickness may be utilized as well. In accordance with theinvention, the source of illumination is located remotely from thedisplay device, such as an LCD and its accompanying waveguide, viewscreen, and backlight (if the display device is transmissive). Thedisplay device may be emissive, transmissive or reflective. The displayis described below from the optical and mechanical point of view.

[0053] A schematic block diagram of a flat panel display system 5 inaccordance with the present invention is shown in FIG. 1A, whileportions of display system 5 are illustrated in FIGS. 1B, 1C, 2A and 2B.As will be described, such portions comprise peripherals that will beincluded in a remote enclosure, i.e., away from the display device. Itshould be understood that display system 5 is schematic in nature andthe relative sizes, positions, and shapes of the components in thediagram are merely for ease of discussion.

[0054] As shown in FIGS. 1A-C and 2A and B, display system 5 includes alight-collecting assembly 20, which will be described in greater detailwith reference to FIGS. 4A, 4B and 5-7, for focusing light from lightsource 12. Generally, light-collecting assembly 20 is designed todeliver visible light to its exit ports, although assembly 20 may bedesigned, alternatively, to deliver radiant fluxes, such as infrared(IR) light, ultraviolet (UV) light, and microwaves. Illustratively,light-collecting assembly 20 is approximately 3″ by 4″ by 3.6″ high, andhas a collection efficiency exceeding 70%. Its functional elementsinclude an enclosed concentrated light source 12, such as a small-archigh intensity discharge (HID) lamp and a lamp enclosure comprisingellipsoidal mirrors 10. The light source 12 may be powered by a 270 Warc lamp, which may have an arc gap of 1.4 mm, although other lamppowers and/or arc gaps can be utilized. In addition, light source 12,except for electrode shadowing effects, is preferably a substantiallyomnidirectional radiator. Thus, the collecting assembly 20 canpreferably provide two or more light outputs, by segmenting the outputof omnidirectional light source 12.

[0055] As best seen in FIGS. 1B, 1C and 2A, the ellipsoidal mirror 10are supported by a plurality of L-shaped support brackets 115. Each wingof the “L” is approximately 0.9″ wide and 2.25″ high. Specifically,FIGS. 1B and 1C show an assembly of four L-shaped support brackets 115,while FIG. 2A shows only two of the existing four brackets 115. As shownin FIG. 2A, each bracket has a pair of clearance through-holes (one oneach side of the “L”) 117, for allowing protrusion of the end ferrule ofeach fiber cable leg 25, and a pair of tapped holes 119 for securingeach protruding fiber cable leg to its respective adjuster 120 by meansof thumb screw clamp 18 shown in FIGS. 1B and 1C. Through-hole 117 isapproximately 0.36″ in diameter and tapped hole 119 is approximately0.19″ in diameter. Further, light source 12 and the ellipsoidal mirrorsare supported by bottom and top hub plates (14, 16), each havingapproximate dimensions of 3″ by 3.9″ by 0.25″ thick and having adiameter of 4.93″. Further, the height from the top of top hub plate 16to the bottom of bottom hub plate 14, when supporting the mirrors, isapproximately 2.75″.

[0056] To ensure that ellipsoidal mirrors 10 and mirror edge slots 112,which form exit port holes for light-collecting assembly 20, areproperly aligned, it is desirable to build a suitable set of accuratedatum surfaces into the design of the assembly. Efficient lightextraction from the light source depends on such proper alignment. InFIG. 2A, the exploded view of light-collecting assembly 20 illustrateshow various elements of the light engine are assembled and illustratesthe design of the datum surfaces desired for alignment.

[0057] With reference to FIGS. 2A and 4A-4C, there are illustrativelyfour ellipsoidal mirrors 10. The top and bottom of the four ellipsoidalmirrors 10 have cylindrical surfaces that engage cylindrical hubs ofbottom and top hub plates (14, 16), respectively. The ellipsoidalmirrors 10 are securely held against the bottom and top hub plates (14,16), bottom and top hub plates (14, 16) by garter springs 126 thatengage matching torroidal grooves 127 ground into the backs of theellipsoidal mirrors 10. The top and bottom of the light source 12 areheld by means of a cylindrical clamp assembly 28, which is inserted intocircular holes in the bottom and top hub plates (14, 16). These holesare concentric with the hubs and provide sufficient clearance foralignment of the light source 12 with a common focal point located inthe center of the light-collecting assembly 20 and coincident with thecommon axis of both hubs.

[0058] As shown in FIGS. 2A and 2C, a special alignment washer 23 isdisposed around the hub of the top hub plate 16. The top of the specialalignment washer 23 is flat to engage the flat bottom surface of the tophub plate 16 while the bottom face of this washer has a conical taper tomatch the top faces of the ellipsoidal mirrors 10. Clocking alignment ofeach ellipsoidal mirror 10 about the hub axis is provided by notches 140in the top corner edges of each mirror section (see FIGS. 4A-4C).Notches 140 have accurate reference datum surfaces that are normal tothe bottom face of top hub plate 16. There are four raised keyprotrusions 21 from the bottom conical face of special alignment washer23. Key protrusions 21 have eight accurate reference faces designed toengage the corresponding reference datum surfaces of the fourellipsoidal mirrors 10 notches. In order to provide clocking alignmentof mirror edge slots 112 with corresponding through-holes 117 ofL-shaped support brackets 115, a pin through-hole 29 is provided inspecial alignment washer 23 for engaging a corresponding pin in top hubplate 16. The four L-shaped support brackets and their eightthrough-holes 117 are accurately positioned with respect to the top hubplate 16 pin so as to ensure proper alignment of through-holes 117 withmirror edge slots 112.

[0059] Eight relatively tiny coil springs 38 are inserted intocorresponding receptacles 39 in bottom hub plate 14 adjacent to the hub.The conical bottom faces of ellipsoidal mirrors 10 each engage two ofthese springs. Thus, each mirror section is spring-loaded toward top hubplate 16. This spring-loading action ensures that the top and bottominterfaces of special alignment washer 23 between the ellipsoidalmirrors 10 top conical faces and top hub plate 16 is kept in intimatecontact with each other.

[0060] The spring-loading action of coil springs 38 and of gartersprings 126 is an effective means of maintaining critical alignments inthe presence of thermal dimensional distortions caused by heat generatedby the lamp. This spring-loading method avoids producing stresses at theglass mirror interfaces that would crack the mirrors. Such stressesexist in conventional alignment methods that do not accommodatethermally induced dimensional distortions.

[0061] Advantageously, the unit cost of molding accurate glass surfacesis less than the cost of grinding them (and, of course, less than thecost of grinding and polishing them). Therefore, the critical surfacesof ellipsoidal mirrors 10 are preferably molded. These molded mirrorsurfaces include the ellipsoidal mirror surfaces, the top and bottomcylindrical hub interface surfaces, the top and the bottom conicalinterface surfaces, the notched top mirror clocking interface surfaces,and the ellipsoidal mirror 10 edge slot surfaces. To facilitate theglass molding process, all molded surfaces are designed to have draftangles if they are not otherwise shaped and/or oriented to accommodaterelease from the mold. For example, the top and bottom mirror edges arepreferably configured to be conical instead of flat in order toaccommodate easy mold release. For the same reason, the mirror edgeslots 112 are preferably designed to have a draft angle.

[0062]FIGS. 4A, 4B, and 4C are side elevation, isometric, and assemblyviews, respectively, of the ellipsoidal mirrors 10 of light-collectingassembly 20 shown in FIGS. 1B and 1C. As shown in FIG. 4B, eachellipsoidal mirror 10 comprises two ellipsoidal mirror sections 110,which is preferable for ease of manufacture. Accordingly, eachellipsoidal mirror section 110 is positioned in such a way so as to havea first focal point common to all eight mirror sections 110substantially centered on the arc of light source 12. Further, eachellipsoidal mirror section 110 has a second unique focal point, each ofwhich is substantially centered on or near a respective mirror edge slot112 that provides a cylindrical rod entrance port 125 (see FIG. 4C) fora corresponding cylindrical rod 138 (to be described in detail below).Thus, each ellipsoidal mirror focuses the light it intercepts from thearc on the corresponding cylindrical rod entrance port 125 located at ornear the second focal point of this mirror. Note that each mirror edgeslot 112 is aligned with a respective through-hole 117 shown in FIGS. 1Band 1C. Each cylindrical rod entrance port 125 is, e.g., 4 mm indiameter and intercepts light incident at 0.42 NA (numerical aperture).

[0063] As shown in FIGS. 1B, 1C and 4A-4C, there are illustrativelyeight mirror edge slots 112 (one for each ellipsoidal mirror section110) and thus eight corresponding clearance through-holes 117. Note thateach mirror edge slot 112 is formed by a half-hole in a mirror edge.Each ellipsoidal mirror section has two half-holes, one on each side,thus providing four mirror edge slot s 112 and eight rod entrance ports125 in the lamp enclosure. If it is desirable to maximize collectionefficiency of the light engine, the diameter of each cylindrical rodentrance port 125 should exceed the theoretical size of the arc imageformed by the corresponding ellipsoidal mirror section 110. The marginof excess should be designed to accommodate imaging aberrations,distortion of light rays by the glass envelope that encloses the lamparc, and inaccuracies in the fabricated mirror surface shape and in therelative alignment between the mirror, the arc and the cylindrical rod.Enlarging the diameters of each cylindrical rod 138 requires acorresponding enlargement of each mirror edge slot 112 required forlight egress. This reduces the area of the ellipsoidal mirror section110 surfaces which, in turn, reduces light collection efficiency. Theefficiency loss attributable to this reduction in mirror area issignificant when, e.g., the mirror edge slot 112 area is large enough tobecome a significant fraction of the ellipsoidal mirror section 110area.

[0064] Alternatively, it may be desirable to have a somewhat smallerdiameter cylindrical rod 138 to provide a selected degree of compromisebetween light collection efficiency and the concentration of rodentrance port irradiance, which tends to be more intense near the rodcenter than near the rod edges.

[0065] In the design illustrated here, the rod entrance port diameter Dwas chosen to be:

D=(s 2/s 1)G+0.51,

[0066] where s1 is the short distance along the major axis between theellipsoidal mirror and its first (common) focal point, where s2 is thelong distance along the major axis between the ellipsoidal mirror andits second (unique) focal point, and where G is the gap between the lamparc electrodes.

[0067] In this illustrated example, s1=18.5 mm, s2=46.1 mm, G=1.4 mm,and the resulting D is 4 mm. In the above expression for D, (s2/s1)G isan estimate of the largest theoretical arc image size generated byreflection from any portion of the ellipsoidal mirror area. Theadditional 0.51 mm is for margin. As the above expression forcylindrical rod diameter D indicates, the magnitude of D is a strongfunction of mirror design configuration parameters s1 and s2, and of thelamp electrode gap G.

[0068] The illustrated light-collecting assembly 20 design comprisingfour ellipsoidal mirrors 10 formed from eight ellipsoidal mirrorsections 110 is one of many possible alternative design configurations.For example, the collecting assembly could comprise a greater or alesser number of ellipsoidal mirrors disposed about the arc, which wouldall have a common first focal point. As in the illustratedconfiguration, the second focal point of each mirror would be unique andwould require a corresponding unique cylindrical rod entrance port forlight egress. The greater the number of mirrors in the light-collectingassembly, the smaller would be the solid angle intercepted by eachmirror as seen from the arc or from the corresponding cylindrical rodentrance port. This assumes that the mirrors surrounding the arc are allidentical. Thus, these mirrors would each also have identical values ofs1 and s2. The numerical aperture (NA), defined as the sine of themaximum angle of incidence of rays from the mirror on the correspondingcylindrical rod entrance port, is driven by the shape and projected areasize of the mirror functional aperture and by the distance between themirror and this entrance port. The 0.42 NA of the illustrated design oflight-collecting assembly 20 represents a maximum (or nearly maximum)incidence angle of 25° for rays reflected by the mirror to thecylindrical rod entrance port surface. Of course, both the magnitudes ofD and NA depend on the design of light-collecting assembly 20 and on theelectrode gap G. However, for small values of G, the dependence of NA onG is weak.

[0069] The mirrors may be fabricated from materials such as glass ormetal (not shown). Glass surfaces may have a dielectric coating (forminga thin-film cold mirror) that reflects visible light but transmitsinfrared and, possibly, UV light; thus reducing heat dissipation withinthe light-collecting assembly 20, in the cylindrical rods 138, and/orother optics following the cylindrical rods. Metal mirrors may befabricated from diamond-turned aluminum, electro-formed nickel or ahigh-temperature polymer such as Ultem. Metal or polymer mirrors may becoated with aluminum, dielectric thin films, or other highly reflectivecoatings. As with glass mirrors, a dielectric coating can be used onmetal mirrors to reflect visible light. However, unlike the coatingsused on glass mirrors, which transmit infrared light, ultraviolet light,or both, dielectric coatings on metal mirrors are specially designed toreflect visible light while absorbing light outside the visible band.The heat generated by this absorption is then dissipated by conductionthrough the metal structure thus diverting heat from the mirror cavity.

[0070] Referring again to FIGS. 1B, 1C and 2A, light-collecting assembly20 uses its ellipsoidal mirror surfaces to capture and channel theoutput of the light source 12. Light can be distributed from thelight-collecting assembly mirror edge slots 112 by a light guideassembly, such as a plurality of fiber optic cables each of whichfunctions as an optical transmission line. As shown, each of eight suchfiber cable legs or bundles 25 cooperate with a corresponding rodentrance port 125. Each fiber cable leg 25 may be adjusted by arespective adjuster 120, depicted in FIGS. 1B and 1C, to ensure properalignment. Note that each adjuster 120 is aligned with a correspondingfiber adjustment hole 117. Assuming that the number of exit ports is twoor more (e.g., eight mirror edge slots 112 are illustrated), fiber cablelegs 25 can be joined together within ferrule 30 to form a single path.

[0071] As shown in FIG. 2A, the ferrule 30 envelope can be cylindrical,while the fiber bundle exit port aperture of ferrule 30 is square. Thedimensions of ferrule 30 are approximately 1.5″ in length and 0.75″ indiameter. Ferrule 30 is supported by a bracket 32, having dimensions ofapproximately 3.775″ in length, 5″ in width and 2.57″ in depth. Bracket32 similarly has a circular opening at one end and a square opening atthe opposite end.

[0072] Referring now to FIG. 18, to diffuse hot spots and withstand highpower densities, the input of each fiber leg 25 may be coupled to arespective ferrule 142. Each ferrule 142 can be support a thermallyrobust optically transmissive element or light pipe, such as acylindrical rod 138, which can be air-spaced or bonded to theircorresponding fiber bundles. Cylindrical rods 138 may be fabricated fromsolid glass (e.g., LaSFN31) having a high refractive index or from fusedsilica having a low refractive index. Note that the fibers from theeight fiber cable legs that collect light from each mirror edge slot 112can be randomly mixed to provide a level of homogenization before thelight emerges from a single common exit port within ferrule 30 andenters the next stage. An example of a cylindrical rod 138 is shown inFIG. 19. As illustrated, cylindrical rod 138 is 13 mm in length and 4 mmin diameter.

[0073] As shown in FIG. 1A, a beam homogenizer 40, which will bedescribed in greater detail with reference to FIG. 8, receives light atinput 44 from the output of ferrule 30. However, as further shown inFIGS. 1A and 2B, a dimmer 42, such as an iris, a variable neutraldensity filter, sliding apertures, or a liquid crystal shutter, canoptionally precede homogenizer 40, to reduce or eliminate light to thehomogenizer.

[0074] Homogenizer 40 creates a uniform irradiance over thecross-section of the output 46 of the homogenizer. The output of thehomogenizer 40 is coupled to a second optical transmission line, such asan expanding fiber optic cable 50 shown in FIG. 1A, which has one input52 and multiple outputs 54.

[0075] In the example of FIG. 1A, the light from the fiber optic cable50 is coupled to a collimator 60. Collimator 60 may be a long taperedlight pipe having a small area input port and a large area output port,e.g., a square cross section-tapered cone that functionally approximatesa compound parabolic concentrator (CPC), a simple array of one or moresuch elements, or an array of lenses that collimate the light. Theoutput of collimator 60 feeds a waveguide 70 that illuminates a displaydevice 80 either directly or via a turn-the-corner prism assembly 72,which may be provided for the sake of compactness.

[0076] Collimated light is preferable for illuminating certain types ofdisplays. For example, collimated light is desirable for backlightingcertain liquid crystal displays (LCD) because the contrast is highestwhen the light incidence angles on the LCD are confined to a relativelynarrow range. Conversely, diffused or uncollimated light will result inreduced contrast.

[0077] As previously mentioned, if the size or other constraints of thephysical layout of display system 5 requires a change in the directionof the light traveling between the output of collimator 60 and waveguide70, a turn-the-corner assembly 72 (having one or two prisms) may precedewaveguide 70.

[0078] As shown in FIGS. 2A and 2B, many of the components of displaysystem 5 can be placed in an enclosure 900 (and sealed by cover 905),referred to as a remote enclosure. Remote enclosure 900 provides alocation for positioning elements of the display system away from thearea of the display 80, e.g., a panel in a cockpit, where space is at apremium. The dimensions of the remote enclosure may be preferentiallyset to fit unique application requirements. For example, in an aircraft,the remote enclosure can have dimensions defined in the 3ATI, 5ATI orother size standards and thus be mounted in racks utilized by theinstruments to be replaced by this invention. Thus, for the 3ATI sizestandard, the dimensions of the remote enclosure may be approximately 3″by 3″ by 9″. Accordingly, the need for any major structural changes tothe aircraft is greatly reduced. Additionally, components that generatea great deal of heat can be located in the remote enclosure, away fromheat-sensitive elements, where heat removal is more easily accomplished,and where envelope space restrictions are less severe.

[0079] As illustrated, the light source 10, the collecting assembly 20,the dimmer 42, the homogenizer 40, and associated brackets (previouslydescribed), are contained within remote enclosure 900. Fiber optic cable50 connects the output of the homogenizer to the rest of the components(e.g., the collimator 60 and the waveguide 70). In addition, othercomponents of the system, such as a power supply 910, a lamp drive 920,a video interface 930, an input/output module 940, and a processingmodule 950, can also be located in remote enclosure 900. It should beunderstood that depending on the requirements of a particular system andavailable space, one can choose to include or exclude any number ofthese items in or from remote enclosure 900.

[0080] Light-collecting Assembly

[0081]FIGS. 4A, 4B, and 4C show the side, the isometric, and theassembly views of light-collecting assembly 20, respectively, of FIGS.1B and 1C. As stated previously, light-collecting assembly 20efficiently couples light from lighting device 12 to homogenizer 40. Thecollecting assembly segments the output of the lighting device throughthe mirror edge slots 112, optimizing the capture of light and improvingthe efficiency of the system. The isometric view of FIG. 4B shows one ofthe four ellipsoidal mirror sections 10 which comprise the lampenclosure, where each of the four mirrors 10 comprises two mirrorsections 110. Note that each of mirror sections 110 is an ellipsoid ofrevolution about the ellipsoid major axis. Accordingly, collectingassembly 20 has eight ellipsoidal mirrors 110 having a first commonfocal point at the center of the light engine cavity and a second uniquefocal point, not shared with any other ellipsoid, which is at one of theeight mirror edge slots 112 located near the edge of each adjacentellipsoidal mirror 110. As previously discussed, each mirror 110 has ahalf-hole on one side, such that two adjacent mirrors 110 form eachmirror edge slot 112.

[0082] As further discussed with reference to FIGS. 4C, 19 and 20, themirror edge slots 112 can preferably interface with a respectivetransmissive element or optical light pipe, such as solid cylindricalrod 138. This light pipe may be coupled to a fiber optic cable (such asfiber leg 25), to another light pipe or to a solid core optical fiber.

[0083] The rods 138 are formed of a light transmitting material such asglass, fused silica, or sapphire to eliminate hot spots which mightdamage the fiber cable. In addition, to further shield optical fibersfrom the damaging effects of heat and/or UV radiation and to furtherprotect the downstream optics, especially polymer optics and adhesives,the input port face of rod 138 can be coated with a dielectric IR, UVreflecting coating, and/or a visible light transmitting dichromic film.Further, instead of or in addition to such coating, the rods 138 may bemade of a UV absorbing material or may be doped with a UV absorbingmaterial such as cerium.

[0084] Referring specifically to FIG. 18, during operation (prior toreaching the downstream optics interface), the heat from the lightsource is absorbed by each rod and may be conducted out of each rod 138and into heat conducting ferrule (or cell) 142 that supports the rod andserves as a heat sink. Ferrule 142 is preferably formed of a heatconducting material such as copper, aluminum, stainless steel, acombination thereof, or other suitable heat dissipating materials.

[0085] Each cylindrical rod 138 can be secured to its respective ferrule142 by a thermally robust and optically clear adhesive or clamp (notshown). For an adhesive, it is preferable that the adhesive be ablewithstand a sustained temperature environment, which, for an epoxy suchas Epoxy Technology's Epotek 301-2, is as high as 200° C., and that theadhesive has refractive index low enough to maintain total internalreflection (TIR) of the light propagated within the rod material.

[0086] For example, assume that for light rays originating in an airmedium:

[0087] (1) The maximum ray angle of incidence on the polished entranceport face of a solid cylindrical rod is θ.

[0088] (2) The refractive index of the rod medium is N.

[0089] (3) The refractive index of the adhesive on the rod's polishedcylindrical surface is n.

[0090] Then, in order for TIR to prevail for all light rays propagatingwithin the rod, n is required be less than or equal to the square rootof (N2−sin 2θ). Assuming the cylindrical rods 138 are made of LaSFN31glass, for which N=1.88, and the maximum ray incidence angle from airmedium is θ=25°, then the corresponding maximum adhesive index ofrefraction that maintains TIR is n=1.83. Therefore, Epotek 301-2 epoxyis an example of an adhesive that maintains TIR because it has arefractive index of 1.564.

[0091] Alternatively, if the combination of the rod material andadhesive refractive indices causes TIR to fail, then an appropriatelythick low refractive index coating, such as magnesium fluoride (whichhas a refractive index of 1.38) may be applied between the adhesive andthe rod. If, however, a clamp is used to hold rod 138, the lowrefractive index coating is applied between the clamp and the rodsurfaces to form a barrier layer.

[0092] Cooling Arrangements for the Light-collecting Assembly

[0093] If a high-intensity light source 10 (such as a small-arc HIDlamp) or other high-wattage lamps are employed, a cooling system ispreferably incorporated in the system. In the preferred embodiment,illustrated in FIG. 5, assembly 200 includes a light source 12,approximately 3.575″ in length, that is mounted inside a close-fittingtube 210, such that both are positioned on a suitable lamp fixture 220.The tube 210 may be cylindrical or assume any other appropriate shape,and can be fabricated from a clear material with good thermalconductivity, relative to air, such as fused silica or sapphire. Asdepicted, tube 210 is covered on one end by a cover 230 to form anenclosure.

[0094] The outer surface 212 of tube 210 is in physical contact with themirrors 110 of the collecting assembly 20. This allows thermal energygenerated by the light source 12 to flow to the tube 210 and then to thecollecting assembly 20. Alternatively, cooling may be provided byattaching a metal conduit to the glass envelope of the lamp andanchoring the conduit to a heat sink (not shown).

[0095] An alternative light source and cooling assembly 300 is shown inFIG. 6. The assembly 300 has lighting source 12. In this embodiment,light source 12 may be a short-arc, metal halide HID lamp such as a 270W version manufactured by a Japanese company, Ushio America, Inc.Thermal buses 330 of copper or other material having suitable heatconductivity couple the light source 12 at a minimum of two points anddraw heat away from seal areas 350 to heat sinks 340. Each thermal bus330 is approximately 1.07″ long with a diameter of 0.75″. The seal areas350 are typically molybdenum foil conductors, which form a gas-tightseal when the lamp quartz envelope is heated and “pinched.” The thermalbuses 330 are designed such that the foil seal temperatures aremaintained within a range recommended by the manufacturer, above whichthe seal would likely fail. This technique also takes advantage of thepoor thermal conductivity of the foil, where minimal power from the lamppropagates through the thermal bus resulting in a low thermal variance.

[0096] The ellipsoidal light-collecting assembly 20 is also representedin FIG. 6. Heat absorbed by light-collecting assembly 20 will pass toheat sinks 340. To further reduce the foil seal temperature, fillermaterial can be added between the thermal busses 330 and the quartz lamp310 to fill in air voids, as air is a very poor thermal conductor. Thefiller material, however, should allow for the relative movementsbetween the quartz and copper, should have low out-gassingcharacteristics, and should be able to withstand temperatures in excessof those recommended by the light manufacturer (such as 250° C.) inorder to have sufficient safety margins. For example, one can useNuclear Grade Style SW-GTA Grafoil® manufactured by the UCAR CarbonCompany, Inc. of Cleveland Ohio. This Grafoil® material is a flexible,thermally conductive, and compressible graphite gasket material havingan extremely low ash content while containing no binders or resins. Thelack of binders and resins eliminates the possibility of hightemperature-inducing out-gassing, which would risk the condensation ofout-gassing vapors on the colder ellipsoidal mirror 10 surfaces thusdegrading their reflectance efficiency. The entire assembly 300 may beforced-air cooled, provided that air does not impinge on any opticalsurface. As a result, a sealed mirror assembly can be used in relativelydirty environments, such as military and automotive applications. Thecooling airflow rate can be adjusted to maintain temperatures within arange that optimizes lamp life.

[0097] Various other arrangements may be employed. For example, thelight source can be sealed within light-collecting assembly 20 to form aclosed-loop cooling system 400, as shown in FIG. 7. In this embodiment,air is circulated around the outside of the light-collecting assembly.Specifically, light source 12 is enclosed in a sealed collectingassembly 420. Clean air is forced past light source 12 by a fan 422 andthe air is cooled in a plenum 430. The plenum and air conduit togetherforms a sealed assembly, which includes collecting assembly 420. Thesealed space is required to prevent dirty air infiltration from outsidethe sealed space. Optionally, heat sinks, fans or other cooling devices(not shown) can be used to transfer heat away from the plenum 430.

[0098] In another arrangement (not shown), the lamp itself may beforced-air cooled provided that clean air is available. Instead of air,helium or a mixture of helium, neon and nitrogen may be employed to coolthe surfaces.

[0099] Dimmer

[0100] As stated, dimmer 42 may be an iris, a variable neutral densityfilter, sliding apertures or a liquid crystal shutter. As shown in thedetail of FIG. 3, dimmer 42 has two aperture plates 1010, 1020 thatslide horizontally with respect to each other. As illustrated, eachplate has a diamond-shaped aperture 1030. Optionally, there may be afilter, such as an NVIS filter, covering one of the diamond-shapedapertures, which could make a cockpit display compatible with nightvision equipment. By virtue of the small size of this aperture, an NVISfilter located here is far less expensive, thinner, and otherwise farmore compact than an NVIS filter placed in its usual location in frontof and covering the entire LCD display backlight area.

[0101] In operation, as the plates 1010 and 1020 move together or apart,the size of the opening created by the overlap of the two diamond-shapedapertures 1030 varies, as desired. Note that the dimmer is preferablyelectro-mechanical in operation and has a dimming ratio of up to 300:1.

[0102] To attain greater dimming ratios up to (for example) 85,500:1, atwo-stage dimmer can be configured by incorporating two apertures intoone of the sliding aperture plates of FIG. 3. At any given translationalposition of this sliding aperture, only one, of its two apertures, has atransmitting area in common with the aperture in the other (single)aperture sliding plate. The sliding mechanism for this assembly shouldbe designed to move both apertures so as to keep this commontransmitting area centered on the common axis of the ferrule 30 fibercable exit port and the homogenizer 40 entrance port aperture 44. Thisalignment maximizes the homogeneity of the light exiting exit port 46 ofhomogenizer 40.

[0103] The two-stage dimming is accomplished by means of a neutraldensity filter placed over one of the apertures of the two-apertureslide. The first stage of dimming would be accomplished by sliding theclear aperture of the two-aperture slide across the opening of thesingle aperture slide until the minimum size common area opening isreached. For the second stage of dimming, the neutral density filteredaperture of the two-aperture slide is slid across the opening of thesingle aperture slide until the minimum size common area opening isreached again. The neutral density of the filter is chosen such that itsattenuation is equal to, or slightly less than, the maximum attenuationof the first stage of dimming. For example, for a first stage dimmingrange of 300:1, the neutral density could be 2.47, which would provide adimming ratio of 295:1 when the common area of both sliding apertures isat its maximum. The maximum second stage dimming ratio would then be[295×300]:1 or 88,500:1.

[0104] An additional benefit of this two-stage dimming arrangement isthat the NVIS filter can be combined with the neutral density filter onthe other side of the same substrate, thus combining both functions. Theneutral density of the combination would then be designed to be 2.47 inthe example above. This removes the system efficiency reduction normallyattributable to NVIS filters because the first dimming stage isNVIS-free.

[0105] Note that the minimum size limit for the common opening areabetween the two sliding apertures is governed by the increasing level ofdiffraction that occurs as the transmitting aperture becomesprogressively smaller. This diffraction effect can become significantenough to cause decollimation to exceed the numerical aperture (NA)limit of the fibers in the downstream fiber optics cable. This wouldcause light absorption in the cables that would reduce their lighttransmission efficiency.

[0106] Further, even if the fiber numerical aperture (NA) is sufficientto accommodate this collimation loss, a significant decollimation cancause an undesirable alteration in the backlight collimation. The lighttransmission system between the light engine and the waveguide isdesigned to maximize preservation of ètendue and to achieve a certaindegree of collimation of light egress from the waveguide. Appreciabledecollimation by the dimmer minimum aperture size would then result inan undesirable reduction of backlight collimation or in an undesirablechange in performance as the dimming limit is approached.

[0107] Beam Homogenizer

[0108] The beam homogenizer 40, as shown in FIG. 8, can be fabricatedfrom a square cross-section rod that is polished on all six faces.Preferably, homogenizer 40 is made of acrylic, BK7 glass, or othermaterials having low attenuation in the visible light region.

[0109] The square cross-section may be uniform for the entire length ofthe homogenizer or, as illustrated in FIG. 8, may be tapered.Specifically, homogenizer 40 has a large entrance port 44 and a smallexit port 46. The homogenizer may be fabricated by being ground,diamond-turned, laser cut or drawn. Alternatively, a hollow, reflectiveair cavity having a square cross section may be employed. The length towidth ratio of the homogenizer is selected such that the output isuniform at the homogenizer exit port. Length is dependent on thecollimation of the input light, the refractive index of the homogenizermaterial, and the required degree of homogenization. Typically, lengthis in the range of ten times the width. Illustratively, the homogenizer40 has a 13 mm by 13 mm square entrance port and an 8.4 mm by 8.4 mmexit port separated by a distance of 100 mm.

[0110] Further, the length of a tapered homogenizer may be less than thelength of a uniform cross-section homogenizer, while providing the samedegree of homogenization. Thus, a tapered homogenizer is typically morespace-efficient than a homogenizer having a uniform cross-section.

[0111] Fiber Optic Cable

[0112] Fiber optic cable 50, shown in FIG. 1A, includes one commonsquare input port designed to match the size and shape as homogenizerexit port 46. This fiber cable input port is bonded to exit port 46 bymeans of a clear adhesive to minimize loss of efficiency at theinterface by eliminating the air gap and thus reducing Fresnelreflection losses. The fibers emerging from the input port arepreferably bound within a jacketed cable having a nominally circularcross-section. The cable has a sufficient length, two feet for example,to feed the entrance port apertures of collimator array 60 shown in FIG.1A. Thus, fiber optic cable 50 has one common square input port and aplurality of fiber cable exit ports. The transition from the singlejacketed cable to a plurality of jacketed cables can be made at anyconvenient point along the length of the cable. The size and shape ofthe exit ports are designed to be a close match to the collimator arrayinput ports.

[0113] Similar to the single fiber cable input port to the homogenizerexit port interface, each fiber cable exit port is bonded to acorresponding collimator entrance port by means of a clear adhesive,which is used to maximize transmission efficiency at the interface byreducing Fresnel reflection losses. The alignment of the matingapertures at the input and exit ports of the fiber optic cable isimportant to reduce coupling efficiency losses. Such alignment includesensuring that the axes of the mating elements on both sides of theinterfaces are parallel and centered with respect to each other. Inaddition, if the mating apertures are not circular, as is the case forthe square apertures of the homogenizer exit port 46 and the fiber cableinput port, the ports must be rotationally aligned about their commonaxis.

[0114] Further, it is possible to avoid the necessity of implementingextremely tight alignment tolerances by designing the entrance portapertures to be slightly larger than the adjacent exit port apertures.This maintains transmission efficiency by allowing the exit portapertures to slightly under-fill the adjacent corresponding exit ports.This under-fill technique provides the most benefit in cases where themating apertures are smallest at, for example, the interfaces with thesmall collimator input port apertures. This is because smaller aperturesrequire alignment tolerances to be more critical in order to reduce theresulting interface efficiency loss to a given budgeted allowance.

[0115] Array of Collimating Elements

[0116]FIGS. 10A and 10B show examples of collimating elements that couldcomprise collimator array 60 shown in the detailed schematic drawing ofFIG. 9. As shown, the differences between the first collimator 160 andthe second collimator 260 is that in input ports 165 of the firstcollimator 160 are substantially circular, while the input ports 265 ofthe second collimator 260 are substantially rectangular. However, thecollimating elements of both embodiments are tapered in that they eachhave an exit port area larger than its entrance port area. The exit portends are lined up side-by-side to form the array of collimators, such asin collimator array 60 illustrated in FIG. 9. The exit port aperturesare preferably square or rectangular in shape to make it possible tofill the adjacent turn-the-corner prism assembly entrance port aperture,which has a long rectangular shape that spans the array of collimatorexit ports. Filling this aperture with light is important to avoid thedark bands that would otherwise be projected from the resulting areasdevoid of light, through the turn-the-corner prism, into the backlight,and across the display. It is advantageous for the optionally square orrectangular cross-section of the collimator element to be uniform for aportion of its length adjacent to its exit port. This allows the arrayof collimators constructed from these elements be stacked adjacent toeach other with their sides in contact and their axes parallel andnormal to the turn-the-corner prism assembly entrance port face. Suchelements can be easily assembled on a flat surface with their exit portsin contact with the turn-the-corner prism assembly entrance portaperture. This arrangement ensures an easy means of alignment. Thecontacting faces of the collimator exit ports and the turn-the-cornerprism assembly entrance port can be bonded together by means of anoptically clear adhesive, which should have a sufficiently lowrefractive index relative to the prism index to maintain total internalreflection at the adhesive layer interface for light rays reflected bythe prism hypotenuse face.

[0117] First collimator 160 of FIG. 10A shows a plurality of suchelements forming a portion of a linear array that interfaces with amating section of a turn-the-corner prism assembly. Each element has ainput port 165 circular aperture and an exit port 168 square aperture168. The circular input port 165 interfaces with a correspondingcircular exit port of fiber optic cable 50.

[0118] Preferably, the exit port 168 of collimator 160 is 6.6 mm square.This dimension slightly overfills the height of the turn-the-cornerprism assembly entrance port aperture. Thirty-three (33) of these 6.6 mmsquare collimator apertures arranged in a side-by-side tightly packedlinear array are approximately 218 mm long, which is sufficient tooverfill the length of the turn-the-corner prism assembly 72 entranceport aperture slightly. This overfill is desirable to avoid the creationof dark areas or stripes on the turn-the-corner prism assembly entranceport aperture. These stripes are devoid of light and the turn-the-cornerprism assembly could project these stripes into the backlight and acrossthe display. As shown in FIG. 10A, the square cross section portion ofthis collimator element has uniform dimensions of 6.6 mm by 6.6 mm untilit begins to morph with the tapered circular cross section portion. Thetapered portion has a conical shape that increases in diameter betweenthe small circular entrance port and the larger square cross section.

[0119] The second collimator 260 of FIG. 10B shows a plurality ofcollimator elements similar to those of FIG. 10A, which likewise form aportion of a linear array that interfaces with a mating section of aturn-the-corner prism assembly. Each of these elements has an input port265 square aperture and an exit port 268 square aperture. The squareinput port 265 interfaces with a corresponding square exit port of fiberoptic cable 50.

[0120] Similar to exit port 168 of the first collimator 160, exit port268 is preferably 6.6 mm². Thus, its interface with the turn-the-cornerprism assembly 72 entrance port aperture and its overfill properties areidentical with that of collimator 160.

[0121] The tapered portion of each collimator element of the secondcollimator 260 has a square cross-section that increases in size betweenthe small square entrance port and the larger uniform square crosssection region. Thus, instead of having the conical tapered sectionshape of each collimator element in the first collimator 160, theelements of the second collimator 260 each have a pyramidal shapedtapered section.

[0122] The design of the first collimator 160 is preferred over thedesign of the second collimator 260 because if the second collimator 260is used, the fiber bundles of fiber optic cable 50 would be required tomatch the square input port 265 of the second collimator 260. Note thatfiber bundles having square exit ports are more expensive and moredifficult to fabricate than those with round ports.

[0123] A typical length for either the first collimator 160 or thesecond collimator 260, having a 6.6 mm square aperture, is 100 mm. Atypical input port 165 of the first collimator 160 may have a diameterof 1.65 mm. A typical input port 265 of the second collimator 260 may be1.462 mm². These typical input port sizes for both collimators wouldpreferably have an equal input port area of 2.14 mm². Similarly, theiridentical 6.6 mm² exit port aperture areas of 43.56 mm2 are also equal.

[0124] The conical half angle of light entering the input port aperture,of both collimators 160 and 260, from the fiber bundle exit port offiber optic cable 50 has an air-equivalent value of 35°. By applicationof Snell's law, the actual half-angle within a medium having arefractive index of N is given by ψ, where ψ=arcsine{(sin 35°)/N}. Inaccordance with principle of ètendue conservation in an “ideal” system,the relationship of air-equivalent collimation half angles of lightentering and light leaving the collimator ports is:

A_(in) sin²θ_(in)=A_(out) sin²θ_(out),

[0125] where A_(in) and A_(out) are the input and output port areasrespectively, and where θ_(in) and θ_(out) are the correspondingair-equivalent light input and light egress conical half-angles,respectively. Calculating the value of θ_(out) when A_(in)=2.14 mm²,A_(out)=43.56 mm², and θ_(in)=35°, yields a corresponding ideal value ofθ_(out) of 7.3°, which is achievable by a properly configured compoundparabolic concentrator (CPC) used as a collimator element. However, morerealistically, the θ_(out) actual value for collimators 160 and 260,which approximate the performance of the ideal CPC, would be about 9° or10°.

[0126] Another embodiment of a collimator is shown in FIG. 11. Inparticular, a packed triangular air cavity array 1110 includes aplurality of tapered air cavities 1112 having right triangularcross-sections in a plane normal to an axis that bisects the hypotenuseface. As shown, the array is sandwiched by hypotenuse face mirrors 1114.This embodiment functions in the same manner as a square array, sincethe mirror image of the right isosceles triangle, reflected in itshypotenuse face, forms a square. The small seams between each righttriangle are at a 45° angle relative to the top and bottom surfaces.

[0127] Turn-the-Corner Assembly

[0128] As previously stated, it may be necessary to redirect the light(due to space constraints) from collimator 60 before it enters waveguide70. FIGS. 12 and 13 illustrate turn-the-corner assembly 72, where FIG.12 shows greater detail and FIG. 13 includes waveguide 70.

[0129] Turn-the-corner assembly 72 of FIGS. 12 and 13 includes twoprisms 510 and 520 separated by an optional transmissive spacer element530. By adding spacer element 530, it is possible to increase the gapbetween the input and output light bundles. The gap can be adjusted tothe desired size by varying the spacer thickness.

[0130] Prism 510 includes a first face 512, a second face 516perpendicular to face 512, and a mirrored hypotenuse face 514.Similarly, prism 520 includes a first perpendicular face 526, a secondperpendicular face 522, and a mirrored hypotenuse face 524. All faces ofthe prism and of the spacer, including their end faces, are polished.The dimensions of the prisms and the spacer may be designed so as tocapture and transmit light with maximum efficiency. For example, firstand second faces of prisms 510 and 520 may be 6 mm, while the hypotenuseface of prisms 510 and 520 may be 8.49 mm.

[0131] Prisms 510, 520 and spacer element 530 may be formed of atransparent polymer material such as acrylic or polycarbonate.Alternatively, glass, such as fused silica, F2, or BK7 can be used, aswell as a combination of these materials. If necessary, the prismhypotenuse faces can be coated with aluminum, silver, a multilayerdielectric film, or other mirror coating 542. Alternatively, asufficiently high refractive index material, such as LaSFN31 glass, canbe used to form the prisms and spacer element, which eliminate the needfor a mirror coating by maintaining TIR for the entire range of lightray angles incident on the prism hypotenuse air/glass interfaces. Forexample, the hypotenuse faces of right angle prisms made of LaSFN31glass, which has a refractive index of 1.88, will completely internallyreflect all light rays incident on the prism entrance port from airmedium at angles of 24.5 degrees or less.

[0132] The prism entrance and/or exit port faces may, optionally, bebonded to adjacent transmissive elements, such as the waveguide 70entrance port and/or the collimator 60 array exit port, by means of aTIR-maintaining adhesive having a refractive index sufficiently lowerthan that of the prism material. When the turn-the-corner prism assemblyentrance port has a refractive material interface instead of air, theentrance port incidence angle for determining whether TIR is maintainedon the hypotenuse face is the air-equivalent angle rather than theactual angle.

[0133] As an example, in operation, and as shown by the dotted-lineexamples a, b, c, light enters the entrance port of assembly 72 at thefirst perpendicular face 512 of the first prism 510. The rays of lightreflect off mirrored face 514 and passes out through secondperpendicular face 516. Thereafter, it passes through the spacer 530 andenters second perpendicular face 522 of the second prism 520, reflectsoff mirrored face 524, passes out through first perpendicular face 526,and is then transmitted to waveguide 70.

[0134] An interface adhesive 540, having a low index of refraction, maybe placed between each adjoining surface to improve the light-handlingefficiency of the assembly. Depending on the physical layout of thecomponents in a given application and the degree of redirectionrequired, the first prism 510 and/or the spacer 530 may be omitted. Ifboth are omitted, the light input port for the turn-the-corner prismwould be at the second perpendicular face 522 of prism 520. If onlyprism 520 is omitted, light would enter through the bottom of spacer 530on the face parallel to second perpendicular face 522.

[0135] Waveguide Assembly

[0136] As previously discussed, light is transmitted to display device80 via waveguide 70. Waveguide 70 is shown in detail in FIG. 14. Asillustrated, waveguide 70 has a relatively thin planar structure, havinga front surface 802, a back surface 804, and two edge surfaces 806 and808. The approximate dimensions of waveguide 70 are 162.5 mm by 215 mmby 6 mm thick. The waveguide is preferably acrylic and has a refractiveindex of 1.485, although materials such as glass or other opticalpolymers may be used.

[0137] In operation, collimated light is injected at normal incidenceinto one or both of the edge surfaces 806 and 808. As light travelsinward from the edges 806 and 808 toward the center of the waveguide800, non-smooth surface features (on the back surface 804) redirectslight toward the front surface 802, causing the light to exit the frontsurface at a predetermined angle relative to the normal to the surface802. Inventive back surface features will be later described withreference to FIGS. 15 and 16 vis-a-vis the conventional back surfacefeatures illustrated in FIG. 17.

[0138] A thick low-index coating (not shown) may be placed between thewaveguide and an underlying aluminum or protected silver reflectivelayer (not shown) to maximize the use of TIR. Additionally, a broadbandretarder and reflective polarizing film (not shown) can be placed on thefront surface 802 of waveguide assembly 70. Suitable films arecommercially available from Japanese company NittoDenko, America, Inc.of Fremont, Calif. Such films pass light of one polarization, butreflect light of the opposite polarization. The reflected light willundergo two quarter phase shifts (the first for the first pass-throughfrom the retarder film and the second upon being reflected by thealuminized coating) and return through the retarder film.

[0139] The front surface 802 and the four edge surfaces 806 and 808 maybe flat, while the back surface 804 may have surface features designedto redirect the received collimated light. For example, a conventionalsurface, shown in FIG. 17, comprises an array of steps or terraces thatare parallel to front surface 802. However, the purely terraced surfacesof FIG. 17 have disadvantages in relation to the inventive sawtoothbottom waveguide surface of FIG. 15 and the inventive truncated sawtoothbottom waveguide surface of FIG. 16, as will be discussed below.

[0140] The inventive sawtooth pattern bottom surface for waveguide 70 isshown in FIG. 15. As shown, light enters the input port face on oneside. The sawtooth extraction features on the bottom face are showngreatly enlarged from their actual size for illustration purposes.Illustratively, the height of each sawtooth is approximately 0.195 mmand the pitch of the sawtooth array is approximately 0.39 mm. In thisembodiment, all light rays that are intercepted by the bottom sawtoothedarray are extracted. Further, in operation, the array redirects lightout of the waveguide at predetermined angles based on the size and shapeof the horizontal sawtooth surface.

[0141] A staggered or truncated-sawtooth pattern bottom surface forwaveguide 70 is illustrated in FIG. 16. This surface has sawtoothfeatures staggered on a series of terraces that are parallel to frontsurface 802. Illustratively, the height of each sawtooth isapproximately 0.039 mm and the pitch of the sawtooth array isapproximately 0.39 mm. The terraces may be mirror-coated with materialssuch as an aluminized coating to prevent refraction through the slopedsurfaces. The design of the surface features is critical to maintain thedesired exit angle, to preserve collimation of light traveling throughwaveguide, to maintain the spatial uniformity of light exiting throughthe front surface, and to simplify manufacture. In particular, spatialnon-uniformities, such as those caused by waveguide material extinctionproperties can be compensated for by varying the pitch of the lightextraction features or their step height.

[0142] Most of the light on the sawtooth terraced faces in FIG. 16 isreflected by “totally internal reflection” (TIR), so that it re-reflectsthe light to the top face, after which the light has an additionalopportunity to be intercepted and extracted by a sloped facet. In thismanner, each ray entering the waveguide “runs the gauntlet” of terracesand sloped facets until it is either intercepted by a sloped facet andextracted or it exits the thin end face of waveguide 70.

[0143] The truncated-sawtooth design of FIG. 16 is significantly betterin performance than the conventional stepped or terraced surface designs(e.g., of FIG. 17) since such surfaces have two 45° corners per step forthe light to strike head-on. Conversely, the truncated sawtooth-patternsurface has only one 45° corner per step for light to strike head-on.Further, since the corners of the conventional terraced surface cannotbe manufactured as “dead-sharp,” the light will decollimate oncestriking head-on a “rounded” corner. Analysis has shown that theserounded corners make up almost 50% of the decollimation of light. Thus,a lesser percentage of rounded corners is desirable, as occurs with thetruncated-sawtooth design of FIG. 16.

[0144] The slope angles of the sawtooth faces of FIGS. 15 and 16 areillustratively at a 45° angle relative to the waveguide front surface802. They are also “clocked” around display 80 normal, such that thelines formed by the intersection of the sawtooth faces with each other(in FIG. 15) or with the sawtooth-terraced faces (in FIG. 16) areparallel to the waveguide entrance port edge face. This arrangementproduces a direction of propagation for the light extracted from thewaveguide that is perpendicular to waveguide front surface 802.

[0145] However, some LCDs have other preferred directions of lightpropagation for maximizing contrast that differs from the display'snormal direction. Therefore, to maximize contrast in a display, it isalways desirable to match the propagation direction of light extractedfrom the waveguide to the direction of optimum propagation (otherwiseknown as the “sweet spot”) for a given LCD display.

[0146] By varying the sawtooth face angle from 45°, the extracted lightpropagation direction can be varied from that which is perpendicular tothe waveguide front surface 802. Without varying the “clocking” angle ofthe sawtooth features, the relationship between the sawtooth facedeviation angle θ from 45 degrees and the propagation directiondeviation angle ψ to the perpendicular to the waveguide front surfaceis:

θ=(½)sin⁻¹((sin ψ)/n),

[0147] where n is the refractive index of the waveguide material. Thisapplies for ψ variations in the plane containing both the normal to thewaveguide front face and the propagation direction of the light enteringthe waveguide.

[0148] For ψ variations not in the plane containing both the normal tothe waveguide front face and the propagation direction of the lightentering the waveguide, it is necessary to rotate or “clock” thesawtooth features around the waveguide front face normal. In this casethe desired ψ is a function of both “clocking” angle β and sawtooth facedeviation angle θ from 45 degrees.

[0149] The illumination portion of the invention may be used in a widevariety of applications, including, but not limited to, vehiclelighting, search lights, task lights and projection systems. The displaysystem can be utilized in vehicle applications, such as an airplanecockpit, as well as other applications where viewing angles, space,thermal, and/or structural issues are of concern.

[0150] List of Acronyms Used in the Detailed Description of theInvention

[0151] The following is a list of the acronyms used in the specificationin alphabetical order. ATI Air Transport Indicator (standard instrumentsize) CPC compound parabolic concentrator D rod entrance port diameter Ggap between lamp arc electrodes fL foot-Lambert G gap between lamp arcelectrodes HID high intensity discharge (lamp) IR infrared (light) LCDLiquid Crystal Display mm millimeters n refractive index (of rod medium)N refractive index (of adhesive) NA numerical aperture s1 short distancealong the major axis (of an ellipse) s2 long distance along the majoraxis (of an ellipse) TIR total internal reflection UV ultraviolet(light) θ maximum ray angle of incidence

[0152] Terminology Used in the Detailed Description of the Invention

[0153] The following terminology, listed below in alphabetical order, isused throughout the specification.

[0154] Snell's Law The law of internal reflection.

[0155] Alternate Embodiments

[0156] Alternate embodiments may be devised without departing from thespirit or the scope of the invention.

What is claimed is:
 1. An optical array comprising: (a) a plurality oftapered side-by-side cavities geometrically defined as five-sidedpolyhedrons wherein each polyhedron is comprised of two opposinglyparallel similar right isosceles triangular surfaces and threetrapezoidal surfaces, wherein each of said trapezoidal surfacescomprises two opposing parallel sides, and each side of one of saidtriangular surfaces is connected to a corresponding said parallel sideof one of said trapezoidal surfaces; (b) each of each of saidtrapezoidal surfaces being a smooth specularly reflective surfaceadapted to reflect a portion of the electromagnetic spectrum; (c) eachof the two triangular surfaces of each one of said cavities being openend-apertures of that cavity; (d) said optical array having a planarsurface, wherein said planar surface of said optical array is formedfrom the combination of trapezoidal surfaces of adjacent cavities withinsaid optical array; (e) said planar surface of said optical array beingcapped by a common smooth specularly reflective flat surface; and (j)said two opposingly parallel similar right isosceles triangular surfacesof each one of said cavities being perpendicular said planar surface ofsaid optical array.
 2. The optical array of claim 1 wherein the smoothspecularly reflective flat surface is comprised of a reflectivesubstrate with a reflective surface facing toward the adjacent cavitiesthat form said planar surface.
 3. A collimated light distribution systemcomprising: (a) a source of collimated light; and (b) a waveguideresponsive to said collimated light, wherein the waveguide furthercomprising: (i) a pattern surface including microstructured features forextracting the collimated light propagating within the waveguide, and(ii) where the patterned surface is clocked about its normal to modifythe propagation direction of the light extracted from the waveguide. 4.The collimated light distribution system of claim 3 wherein themicrostructured features of said pattern surface have a sawtoothedconfiguration.
 5. The collimated light distribution system of claim 3wherein the microstructured features of said pattern surface have atruncated sawtoothed configuration.
 6. The collimated light distributionsystem of claim 3 wherein the microstructured features of said patternsurface have a terraced configuration.
 7. In combination, the collimatedlight distribution system of claim 3 and a liquid crystal display,wherein: (a) the collimated light distribution system is used as anillumination source for the liquid crystal display and said patternedsurface of the waveguide is clocked in order to direct the propagationdirection of extracted collimated light in a direction off-normal to aninput surface of said liquid crystal display and through a high contrastviewing angular region of said liquid crystal display.
 8. Thecombination of claim 7 wherein said extracted collimated light isdiffused and projected it to fill a viewing angle range of interest. 9.A mirror coating for the surface of a refractive optical element havinga predetermined refractive index and internally propagating light flux,said mirror coating comprising: (a) a light transmitting low refractiveindex layer having a thickness of at least three wavelengths of apredetermined electromagnetic signal; (b) said low refractive indexlayer being between the surface of said refractive optical element and areflective coating layer; and (c) wherein said low refractive indexlayer having a refractive index lower than the predetermined refractiveindex of said refractive optical element and adapted to promote totalinternal reflection of said internally propagating light flux at aninterface between said mirror coating and said refractive opticalelement.
 10. In combination, the mirror coating of claim 9 and awaveguide including a microstructure light extracting patterned surface,wherein: (a) said light extracting patterned surface is coated with saidmirror coating.
 11. A collimated light distribution system comprising(a) a source of collimated light; (b) a waveguide responsive to saidcollimated light, wherein the waveguide has a pattern of microstructuredfeatures for extracting the collimated light propagating within thewaveguide, and wherein said waveguide further comprises: (i) a mirrorcoating on its microstructured light-extracting patterned surface; (ii)a reflective polarizer over the waveguide surface opposite to itspatterned surface; (iii) a retarder layer between said reflectivepolarizer and the waveguide surface, said retarder layer generatingone-quarter wave rotation; and (d) wherein said waveguide adapted togenerate a substantially polarized collimated light output.
 12. Anoptical alignment apparatus for supporting a plurality of opticalelements that enclose a light source configured to maintain criticalalignments while minimizing thermally-induced stresses, said apparatuscomprising: (a) a central hub, wherein said light source is aligned andsecured to said central hub and each of said optical elements iscompliantly forced to interface against said central hub; and (b)wherein each optical element includes at least one feature that iscompliantly forced to interface against a mechanical structure that isaccurately positioned relative to said central hub.